The present examples relate to an optical information recording apparatus and an optical information recording method.
Optical disc products with a recording density of about 50 GB are being commercialized that are based on Blu-ray Disc (BD) standard and High Definition Digital Versatile Disc (HD DVD) standard using a blue semiconductor laser.
Optical discs are expected to have an increased capacity of as large as 100 GB to 1 TB, comparable to that of HDD (Hard Disk Drive), in the future.
However, to realize such an ultrahigh density with the current optical discs, a novel storage technology is required, different from the conventional trend of high density technologies that attempts to increase the storage capacity by shortening a wavelength and increasing NA of an objective lens.
With wide-ranging studies on next generation storage technologies under way, a hologram recording technology is available that records digital information using holography.
In the holographic technology, data information is recorded through interference patterns of a signal beam modulated two-dimensionally by a spatial light modulator and a reference beam in the holographic storage medium.
Data information is reproduced two-dimensionally by means of CMOS, CCD, or other type of photo detector. These features are effective for large-capacity, high-speed recording and reproduction of information.
Among the hologram recording technologies is one disclosed in JP-A-2004-272268 (Patent document 1). This patent document describes a so-called angle-multiplexed recording method which focuses a signal light flux on an optical information recording medium through a lens and at the same time throws a reference light of collimated rays to the medium to cause interferences to record a hologram and reproduces different pages of data on a spatial optical modulator while changing an incidence angle of the reference light to the optical recording medium to realize multiplexed recording. The patent document also discloses a technology that puts an aperture (spatial filter) at a beam waist of a lens-focused signal light to shorten the intervals of adjoining holograms, thereby increasing the recording density and capacity, compared with those of the conventional angle-multiplexed recording method.
Another hologram recording technology is disclosed in, for example, WO2004-102542 (Patent document 2). This document describes an example of shift multiplexing in a hologram recording method in which one spatial light modulator focuses a light from inner pixels as a signal light and a light from outer ring-like pixels as a reference light onto an optical recording medium through one and the same lens to cause interferences between the signal light and the reference light at near the focus plane of the lens to record a hologram.
Another related art is also found in Japanese Patent Application Laid-open Publication No. 2007-256945-A (Patent document 3). This Patent Document 3 discloses an example of a system to cure a recorded hologram.
In addition, it is known that a “volume” is the actual 3D region on a holographic memory or recording medium, “page” is an interference pattern (2D) recorded at a location within the volume, “page data” is the data to be recorded as 1 page, “book” is an accumulation of pages of data multiplex-recorded on the holographic memory or recording medium, and “a book of data” or “book data” is the data to be recorded as a book on the holographic memory or recording medium.